Starting with your organic intersections, these look pretty solid. You are treating them as 3d forms, and the shadows run along the form of the surface they are being casted on. Only thing I have to say here, is that some of these forms, even though they feel 3d, they look as they were about to fall. In this exercise, you want to start first dropping forms in top of other forms, and imagine how they would drop, and their final position, so that in the final drawing the forms are stable.

Remember that adding lineweight to clarify overlaps between forms is very helpful as well, so don't forget to do it the next times you practice this exercise.

Into your birds, starting with your owl, It looks good, but remember to draw the intersections between all forms, just like you did with the left leg. For the wings, draw the intersection between them as well. And don't approach them like you did, building each individual part. Draw the wing as a single organic form, and then, if you want to add feathers, do it appliying detail with a texture, just like in lesson 2. Marked a few of those things here hoping it would be a little more clear.

On your next page, you are doing a good job in general, good job on the sausage technique, you aren't overdoing contour lines, and the ones you put in help make the drawings specially solid. There's only the feather issue I pointed out before, remember that feathers are a texture, so you should focus only on cast shadows when drawing them, don't draw each one of them individually. I think there's also a tendence to hide construction lines in relation to the other lines in your drawing. Don't do that. Construction lines are just as important as any other line in these exercises. Only add lineweight to your lines when you want to clarify overlaps, or when you want to make clear something is closer to the viewer, with an specific reason.

On your next (lion?) pages, they look pretty solid, but they got a few issues. First one is that you aren't drawing through your forms all the time. I'm sure you are capable of doing that, as you are doing it on the right leg on the second page, but remember to do it through all the drawing. Don't forget to draw the intersections through all your forms neither, just like I mentioned before.

For the organic intersections you add to them, they are following the form, but they lack thickness, which makes them to remain a bit flat. Take a look at the donkey demo to see how to apply the adittional masses correcctly.

The construction of the heads look pretty solid, but don't be afraid do build the muzzle with a complete simple form, like a box, to make clearer the plane changes, and so you can add detail following the form more easily.

Next two drawings are more or less the same, they look solid, but don't forget to apply the sausage technique for the legs, and to draw through all your forms and to draw the thickness of your adittional masses.

This is less important, but for fur, I think you'd benefit by doing more variety of fur lumps, instead of the same small strokes repeated over and over. Take a look at the raccoon demo to see how you could do it.

And for your rhinos, pretty similar too. Try not to overdo the contour lines, and try to make them hook (Just like on lesson 2 organic forms with contour lines) , as some of them are a bit flat, remember contour lines need to accelerate as they get to the end of the forms. Apply as well here the sausage method, and in general, even if you work with other forms, draw through them. I can see improvement on the adittional masses; now they feel like they have thickness, but the bottom one doesn't feel like it wraps much around the form, specially around the part on the back. For the feet even if you simplify them to sausages, I'd at least define top and side planes, so their perspective is clear. Added a few notes here on this.

For the horses again, use the sausage method, and draw through your forms. I can see a bit of overuse of contour lines as well, so remember to be careful with that as well. The adittional mass you added to the head of the horse feels pretty solid as well, only problem I can see there is that the contour line doesn't accelerate enough, good job!

On the crocodile, when drawing the head, remember to break down everything to its most basic forms, for example, you could have simplified the mouth to 2 boxes. You can add detail or more complex forms after it, but by drawing first with the most basic forms, you can be sure the foundation will be solid, and the plane changes will be more clear. For the feet goes the same. Draw through your forms, and build them to basic forms, like sausages or boxes.

The contour lines on them are a bit flat too, same problem I mentioned earlier, hook your contours.

Your whale feels pretty solid excepting the problem with the adittional masses I mentioned earlier. And pretty much the same for the last one, don't hide your construction lines, use the sausage method, and draw through your forms.

Overall I think you're doing a good job with construction, with the main issues I described through the critique:

-Remember to use the sausage form for the legs.

-Draw through all your forms

-Draw the intersection between every form you have in your drawing

-Keep in mind how the adittional forms behave as 3d forms, how they wrap around the body of your subject, and how they have thickness.

-Don't be afraid to simplify everything into its more basic forms, with boxes, cylinders, sausages or other basic form.

-Don't hide your initial construction lines, treat them as if they were part of the final drawing; they are as important as any other line.

I really liked your drawings but I think the susages are meant to sag like water balloons and yours seem too solid. Additionally, I think the way you drew the back legs makes them look very flat.